How to fill PDF form programatically

Why Yes!  There are several ways to pre-fill a PDF.  Which technique depends on where the data comes from and where the PDF is going.

For example, a PDF can be filled in Acrobat using an Acrobat data file such as FDF, XFDF, or XDP if it's a LiveCycle form.  This can be done manually through the menu items or automated with JavaScript, or with a batch process.  And there are lots of other variations on how data files can be used. Of this methodology assumes that the data file already exists.  The data file can be manually created by exporting data from Acrobat or automatically by some external custom program.

Acrobat JavaScript can also used to access Excel and database files:

http://www.pdfscripting.com/public/department48.cfm

and LiveCycle forms can be connected directly to a DB.

http://www.pdfscripting.com/public/34.cfm#XFADBForms

Depending on the kind of data, JavaScript can be used to directly fill in forms.  This method is suiltable for handling a small number of fields, such as customer contact data.

On the server side there is a whole host of third party tools for filling forms and of course Adobe has tools as well.  In fact PDF form data handling is built into ColdFusion.

The Acrobat plug-in SDK has a Forms model for just this purpose and there is an ActiveX interface to Acrobat that can access individual form fields.

Thom Parker
The source for PDF Scripting Info
pdfscripting.com

The Acrobat JavaScript Reference, Use it Early and Often
http://www.adobe.com/devnet/acrobat/javascript.html

Then most important JavaScript Development tool in Acrobat
The Console Window (Video tutorial)
The Console Window(article)